Charge-Carrier Recombination in Halide Perovskites Dane W. deQuilettes1,2, Kyle Frohna3, David Emin4, Thomas Kirchartz5, Vladimir Bulovic1, David S. Ginger2, Samuel D. Stranks3* 1 Research Laboratory of Electronics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA 2 Department of Chemistry, University of Washington, Box 351700, Seattle, WA 98195-1700, USA. 3 Cavendish Laboratory, JJ Thomson Avenue, Cambridge CB3 0HE, United Kingdom 4 Department of Physics and Astronomy, University of New Mexico, 1919 Lomas Blvd. NE, Albuquerque, New Mexico 87131, USA 5 Faculty of Engineering and CENIDE, University of Duisburg-Essen, Carl-Benz-Str. 199, 47057 Duisburg, Germany Corresponding Author *
[email protected] 1 Abstract The success of halide perovskites in a host of optoelectronic applications is often attributed to their long photoexcited carrier lifetimes, which has led to charge-carrier recombination processes being described as unique compared to other semiconductors. Here, we integrate recent literature findings to provide a critical assessment of the factors we believe are most likely controlling recombination in the most widely studied halide perovskite systems. We focus on four mechanisms that have been proposed to affect measured charge carrier recombination lifetimes, namely: (1) recombination via trap states, (2) polaron formation, (3) the indirect nature of the bandgap (e.g. Rashba splitting), and (4) photon recycling. We scrutinize the evidence for each case and the implications of each process on carrier recombination dynamics. Although they have attracted considerable speculation, we conclude that shallow trap states, and the possible indirect nature of the bandgap (e.g. Rashba splitting), seem to be less likely given the combined evidence, at least in high-quality samples most relevant to solar cells and light-emitting diodes.